1. Field of the Invention
The present invention relates to a method and apparatus for making diagnosis of an electrolytic capacitor in operation, and more particularly to such method and apparatus for determining whether or not the electrolytic capacitor functions properly in operation.
2. Description of the Related Art
For example, in a so-called air bag system which is known as one of vehicle occupant protection systems, there is used an electrolytic capacitor called the large-capacity backup capacitor which serves as a backup power source in the air bag system.
This type of electrolytic capacitor is provided in a vehicle to prevent the air bag system from failing in vehicle occupant protection operation due to cut wires occurring in a circuit between a battery and a power supply circuit in the air bag system due to an accident involving the vehicle carrying the air bag system. The cut wires preventing the battery from supplying its power to each of the element circuits of the air bag system. More specifically, the electrolytic capacitor in the air bag system is used in place of the battery when such, cut wires occur due the accident involving the vehicle, and supplies its power to the air bag system to enable the system to normally function.
In consideration of the importance of its purpose of the backup capacitor in use, in most cases, such an electrolytic capacitor is provided in the air bag system together with its diagnosis circuits for determining deterioration in properties of the electrolytic capacitor, and for checking on circuit connections in the air bag system.
For example, deterioration in capacitance of the electrolytic capacitor causes its predetermined supply voltage to decrease, which makes it impossible for the electrolytic capacitor to function as a backup power source in the air bag system. Consequently, checking of such deterioration in capacitance of the electrolytic capacitor is considerably important. In order to perform such checking or diagnosis operation, various types of capacitance checking or diagnosis devices have been proposed, each of which comprise: a booster circuit for producing a charging voltage of the capacitor by boosting a voltage supplied from the battery to a predetermined voltage; a discharging circuit through which the capacitor is forcibly discharged; and, a counter circuit for measuring a predetermined elapsed time.
However, each of the above-mentioned conventional checking or diagnosis devices requires its own circuit in addition to the element circuits of the air bag system, and, therefore raises the manufacturing cost of the air bag system in total. Further, for example, in most cases, the conventional checking or diagnosis device performs its checking or diagnosis operation only when an engine of the vehicle is turned on by its engine key. In other words, any checking or diagnosis operation is not conducted after the engine is started. Consequently, as for the time interval of its checking or diagnosis operation, the conventional equipment is insufficient to properly perform its function.
Furthermore, When a user drives the vehicle, it is impossible for the conventional equipment to determine whether cut wires occur in the circuit between the positive (or the negative) pole of the backup capacitor and the element circuits of the air bag system.